Step Motors
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Step Motors are digital processors that produce information for each specific task at hand, in this case motion control. One may assume that Step Motors will dependably follow digital instructions just as a computer is expected to. This is the distinguishing feature for Step motors.

Step Motors are driven by digital pulses rather than a continous supply of voltage going into the circuit. Inherent in this concept is open-loop control, wherein a train of pulses translates into so many shaft revolutions, with each revolution requiring a given number of pulses. Each pulse equals one rotary increment, or step (hence, Step motors), which is only a portion of one complete rotation.

Therefore, counting pulses allows you to achieve a shaft rotation of your choosing. Each count represents how much movement has been achieved with no feedback information such as servo systems.

Although Step Motors have been overshadowed in the past by servo systems for motion control, Step Motors are now emerging as the preferred technology in more and more areas. The increase of recognition of the Step Motor is due to the development of the microprocessor, and its prevalence of digital control.

Step Motors are now applied in various applications such as, printers (paper feed, print wheel), photo-typesetting, clocks and watches, aircraft controls, disk drives, and many other applications. The ingenuity and further advances in digital technology from researchers will continue to extend the list of applications in which Step Motors will be used.

There are three basic types of Step Motors. The Step Motors types fluctuate by construction and in how they function. Each of these types of Step Motors delivers a solution to an application in a different way. The three basic kinds of Step Motors include the Variable Reluctance, Permanent Magnet, and Hybrid.

Variable Reluctance (VR) Step Motors The Variable Reluctance Step Motors generally rotate with step angles anywhere from 5 to 15 degrees at high rates. Variable Reluctance Step Motors are recognized for its wound stator, and soft iron multiple rotor and wound stator. They also possess no detent torque. In Figure 5, when phase A is energized, four rotor teeth line up with the four stator teeth of phase A by magnetic attraction. The next step is taken when A is turned off and phase B is energized, rotating the rotor clockwise 15 degrees; Continuing the sequence, C is turned on next and then A again. Counter clockwise rotation is achieved when the phase order is reversed.

Permanent Magnet (PM) Step Motors Permanent Magnet Step Motors contain rotors that are magnetized perpendicular to the axis, and further differ from Variable Reluctance Step Motors by also having permanent magnet rotors without teeth for a smoother rotation.When the rotor rotates because of its attraction to the magnetic poles, all four phases have been energized in sequence. The motor shown in Figure 6 will take 90 degree steps as the windings are energized in sequence ABCD. Permanent Magnet Step Motors generally has step angles of 45 to 90 degrees and tends to step at relatively low rates, but develop high torque and outstanding damping characteristics.

Hybrid Step Motors Hybrid Step Motors combine the qualities from the permanent magnet and variable reluctance Step Motors giving the Hybrid Step Motors desirable features.These Step Motors have many great qualities for motion control such as, operating under high Step speeds, high detent torque capacity, and excellent holding and dynamic torque. Step angles of 0.9 to 5.0 degrees are usually seen in Hybrid Step Motors. Bi-filar windings are generally supplied to these Step Motors so a single power supply can be used to power the Step Motors.The rotor will rotate in increments of 1.8 degrees if the phases are energized one at a time in the order they are indicated at. These Step Motors can be driven in two phases at a time to yield more torque. Hybrid Step Motors can produce half steps of 0.9 degree increments of rotation when driven by one then two the one phase.

There are three excitation modes that are normally used with Step Motors. The Step Motors modes are the full-step, half-step and micro-step.

Step Motors - Full-Step In full step operations, Step Motors step through the normal step angle e.g. 200 step/revolution motors take 1.8 steps while in half step operation, 0.9 steps are taken. The Step Motors full phase mode has two types, single phase and dual phase. Single phase full-step mode happens when the Step Motors are operated one phase energized at-a-time, but this mode can only be used when high speed performance and a high torque rating are not important. For example the motor is operated at load conditions that are well defined and has a fixed speed of rotation. This mode requires the least amount of power use from the drive power supply of any excitation modes, but any problems with the resonance can prohibit the Step Motors to operate at a number of speeds.Dual phase full-step excitation happens when the Step Motors operate with two phases energized at once. Providing you with good speed performance and good amounts of torque with maintaining minimal resonance problems. Dual excitation generates about 30 to 40 percent more torque than a single excitation, but in order for dual excitation to function correctly it needs twice the power from the driver.

Step Motors - Half-Step Step Motors have half-step excitation which is alternate single and dual phase operation resulting in steps one half the normal step size. This mode provides twice the resolution.This mode has become the predominately used mode by Anaheim Automation because it offers nearly complete freedom from resonance problems. The Step Motors output torque does vary on alternate steps to offset the need to step through only half the angle. These Step Motors can operate over a wide range of speeds and used to drive almost any load generally encountered.

Step Motors - Micro-Step In Step Motors micro-step mode, a Step Motor's natural step angle can be divided into much smaller angles. For example, if you want to move the Step Motors at 0.18 degrees with 2,000 steps/revolution, you need a standard 1.8 degree motor that has 200 steps/revolution, and divide it by 10.Typically micro-step mode ranges from divide-by-10 to divide-by-256 (51,200 steps/rev for a 1.8 degree motor). Each step is produce by proportioning the current in the two windings according to cosine and sine functions. This mode is required when your system needs a smoother rotational motion.

Step Motors are typically controlled with a indexer and driver to evaluate the amount of speed and direction of the rotational motion of the Step Motors. The main types of control devices for Step Motors are: Step Motors Drivers, Step Motors Control Links, and Step Motors Controllers. These devices are set up in figure 8.The Step Driver accepts the clock pulses and direction signals and converts these signals into proper phase currents for the Step Motor. The Step Indexer creates the clock pulses and the direction signals for the Step Motors.The computer or PLC (Programmable Logic Controller) sends out commands to the indexer.

Anaheim offers a wide variety of products such as Step Motors that can be customized to fit your specific needs. Some examples of customization are, shaft, oil seal for an IP65 rating, brake, speed, mounting dimensions, torque, and voltage.For any questions that you may have for customizing our Step Motors for your applications, please feel free to get in touch with our engineers at Anaheim Automation.

Problem: Intermittent or erratic driver function. Solution: This failure is the most common and one of the most difficult to detect. You would start by making sure that all your connections are tight. Evidence of discoloration at the terminals/connections, may indicate a loose connection. When replacing a step motor, driver or Driver Pack in a motion control system, be sure to inspect all terminal blocks and connectors. Check cabling/wiring for accuracy. Stress wires and connections for worse conditions and check with an ohmmeter.

Problem: Motor wires were disconnected while the driver was powered up. Solution: When this occurs avoid performing any service to Step Motors or drivers while the power is on, especially if there are problems with the Step Motors connections. This is imperative for both the technician/installer, as well as the driver.

Problem: Poor system performance. Solution: To make sure that the wire cables are not to long keep the lengths under 25 feet when connecting to the Step Motors.When the length of the wiring exceeds over 25 feet, contact Anaheim Automation for instructions regarding the likelyhood that transient voltage protection devices are required. Another possibility is that the motor lead wires are of a gauge that is too small. Do not match your cable wires to the gauge size the step motor lead wires.Anaheim Automation suggests that for such wiring, a shielded cable (purchased seperately) is necessary. Additionally, you need to check the age of the Step Motor that is in use, over time the Step Motors lose some of their magnetism which affects its performance.A typical life span for a step motor is expected to be about 10,000 hours (4.8 year, running eight-hour shift per work day). Also, make certain that your step motor and driver combination is a good match for your application. Contact the factory, should you have any concerns.

Problem: The step motor has a shorted winding or a short to the motor case. Solution: You are likely to have a defective Step Motor, and repairs for this issue are not to be attempted.If the Step Motors case is opened it may de-magnetize the motor, and cause the Step Motors to have poor performance, and will also void your warranty.The motor windings can be tested with an ohmmeter. As a rule of thumb, if the step motor is a frame size of NEMA 08, 11, 14, 15, 17, 23, or 34 and the warranty period has expired, it is not cost-effective to return the step motor for repair.Call Anaheim Automation if you suspect a defective Step Motor if it is a NEMA size 42 or a K series motor, or if the Step Motor is still under warranty.

Problem: The step motor driver or Driver Pack is over-heating. Solution: Ventilation and cooling are essential - failure to provide adequate airflow will affect the step motor driver’s performance and will shorten the life of the driver. Keep driver temperatures below 60 degrees Celsius.To insure that good air flow is maintained, use fans, base plates, and heat sink material just to be sure that you do not exceed the maximum temperature of the Step Motor, driver, or controller. Also be aware of the temperatures inside cabinets and enclosures where Step Motor drivers may be placed.

Problem: Environmental issues are less than ideal. Solution: Environmental factors such as, welding, moisture, chemical, humidity, etc. These things can damage both the electronics and the Step Motors. Protect the Step Motor and the driver from environments that contain voltage spikes, that are corrosive, or prevent good ventilation. Anaheim Automation offers you products that have several line voltage ranges. For AC lines that contain voltage spikes, a line regulator (filter) will likely be required.

Problem: Pulse rates (Clock or Step) to the driver are too high. Solution: The typical half-step driver can drive the step motor at a maximum rate of 20,000 pulse per second. Pulse rates of above 60,000 pulses per second can damage the driver. See individual specification sheets for the motor and driver combination for best performance.

Problem: The step motor is stalling. Solution: Some drivers are manufactured to protect itself from voltage spikes. But in some cases stalling the motor causes a large voltage spike that will often have a high probablity of damaging the phase transistors on the driver. Transient Suppression Devices can be added externally, contact Anaheim Automation for additional information that you may need.

Problem: The step motor is back-driving the driver. Solution: Step motors that are being turned by a load create a back EMF voltage on the driver. Higher speeds will produce higher voltage levels.If you allow the rotational speed to get to high this voltage might damage the driver, especially if the Step Motor is back-driven while the driver is still on.Put a mechanical stop or brake in applications that might be subject to these phenomena.

The following safety considerations must be observed during each phases of operation of your applications. If you fail to comply with these precautions, you violate the safety standards of design, intended use, and manufacture of the product. Anaheim Automation, Inc. assumes no liability for the customer’s failure to comply with these requirements. Even well built products, operated or installed improperly, can be hazardous. Safety precautions must be observed by the user with respect to the load and operating environment. The customer is responsible for proper selection, installation and operation of the products purchased from Anaheim Automation, Inc.

• Use caution when handling, testing, and adjusting during installation, set-up and operation
• Service should not be performed with power applied
• Exposed circuitry should be properly guarded or enclosed to prevent unauthorized human contact with live circuitry
• All products should be securely mounted and adequately grounded
• Provide adequate air flow and heat dissipation
• Do not operate in the presence of flammable gases, vapors, liquids or dust

NOTE: Please Use a RMA Form should you need to return a product for REPAIR. This form can be found in Support, Forms, RMA Request on this web site.

Basic Overview of a Stepper Motor

Currently, Step Motors are used everywhere most often in manufacturing plants for a wide range of purposes. They are most useful because of their ability to provide constant power. Step Motors have been in use for many years and are continually being put into use around the world. Step Motors run at low rpm speeds to achieve a high amount of torque that would not be possible running at higher speeds. The three types of Step Motors are the variable-reluctance, the permanent-magnet, and the hybrid step motor. Each one of the Step Motors has different characteristics for specific uses, and are most often used to position objects. Examples of where you would see Step Motor in use are with conveyor belts, laser cutting, drilling and grinding machines, and assembly lines.

Step Motors are effective when put to use in assembly lines because assembly lines require precise movements in placing things quickly, with no necessary feedback given about the position. The majority of Step Motors are an open loop system, and the position is known by keeping track of the input step pulses.

Precise positioning is another ideal place where Step Motors are put to use. Step Motors are able to perform detailed movements and positions and offer power while remaining compact; allowing the Step Motors to take on a large workload for a long duration of time. Escalators are a great demonstration of the step motors ability to do this. They must carry a wide range of loads, sometimes even thousands of pounds, and remain at constant speed.

Step Motors have many additional advantages beyond their wide range of uses and precise response time. The input pulse of the Step Motors is proportional to angle rotation allowing for different rotation speeds being available. At a stand still, the motor has full torque if the windings are energized. Step Motors are also more cost effective because of the use of open-loop control. Finally, no brushes within the motor make it a more reliable machine.

Its wide range of applications and characteristics make Step Motors the right choice over other motors in many occasions.